Various cementitious materials are known to be used to prepare a number of different construction products. The cementitious material is normally combined with water and other additives as desired to form a cementitious slurry. The cementitious material is either reacted with water in a hydration reaction to allow for setting to occur in a desired shape, or the water is otherwise dried off to allow the aqueous cementitious slurry to harden in the desired geometry. Examples of such cementitious materials include fly ash, Portland cement, stucco (calcium sulfate hemihydrate in alpha or beta forms, or calcium sulfate anhydrite), and various forms of gypsum (calcium sulfate dihydrate), including landplaster and synthetic gypsum (typically as a by-product of flue-gas desulfurization at coal-fired power plants), and the like.
Such cementitious materials are used in forming construction products such as gypsum drywall used for interior walls and ceilings of buildings, acoustical tile, floor underlayments and capping, mold-resistant board, cement board, and exterior sheathing, to name just a few.
To reduce density in various cementitious products, it is known to introduce air bubbles into the cementitious slurry. If kept stable, the air bubbles transform into air voids when the product is dried. The air bubbles can be introduced in the form of foam prepared generally in a foam generation system as known in the art. Detergent, or soap, surfactants are diluted with water and combined with air in such foam generation systems. The detergents are employed to address the stability of the air bubbles by reducing the surface tension of liquid surrounding them. The foam containing air, water, and detergent is then added to the cementitious slurry to reduce density of the final product.
Existing foaming systems for use in preparing cementitious products have not proven to be fully satisfactory. Foam stability is often problematic, as foam can be wasted as bubbles break up in the slurry because of shear forces or contact with solids in the slurry. In addition, it is difficult to deliver other ingredients with the foam because the other ingredients can destroy air bubbles, thereby compromising efficiency in the manufacturing process.
Thus, there remains a desire for new techniques for introducing foam into cementitious slurries for making various construction materials.